1. Field of the Invention
This invention relates to nucleating agents made from neutralized dimer or trimer carboxylic acids for crystallizable polymers. Nucleating agents of this invention are particularly useful for the crystallization of saturated polyester, such as polyethylene terephthalate.
2. Description of the Prior Art
It is known to use nucleating agents in crystallizable polymers, such as linear saturated polyesters of aromatic dicarboxylic acids. U.S. Pat. Nos. 3,435,093, 3,516,957 and 3,639,527, as well as Dutch Pat. Nos. NL 79-01609 and NL 79-01605, disclose various approaches to molding thermoplastic compositions of linear saturated polyesters of aromatic dicarboxylic acids, and are particularly applicable to polyethylene terephthalate. These patents generally disclose the use of salts of hydrocarbon and polymeric carboxylic acids as nucleating agents for linear saturated polyesters. Great Britain Pat. No. 1,315,699 discloses the use of low molecular weight sodium, lithium or barium salts of mono- or polycarboxylic acids used with solid, inert inorganic substances.
A molding formulation based on a linear saturated polyester, such as polyethylene terephthalate, should result in molded product having good physical properties including flexural strength, modulus, tensile strength and impact properties. Further, the molding compound should also have good molding properties, including a melt flow index for sufficient flow into the mold, good mold release properties and good finished appearance.
From a practical point of view, it is desirable that satisfactory properties, as outlined above, be attained using water heated molds. That is, molds heated to temperatures between 76.7.degree. C. (170.degree. F.) to about 100.degree. C. (212.degree. F.). In order to accomplish this, it is desirable for crystallization to begin at as high a temperature as possible upon the cooling of the polyester which was fed into the mold, and continue during the cooling to as low a temperature as possible. T.sub.cc is a measurement to determine at what temperature crystals first appear upon cooling from the melt. T.sub.ch is a measurement which indicates the temperature at which crystallization is no longer occurring upon cooling. It has been found that mold appearance and mold release properties can be related to T.sub.ch. T.sub.ch is determined by measuring the temperature at which crystals appear upon heating an amorphous piece of polyester. T.sub.cc and T.sub.ch can be measured using a Differential Scanning Calorimeter.